The present invention relates generally to explosive charges and, more particularly, to the melt casting of explosive charges with high solids content.
In melt-cast loading of shaped charges with trinitrotoluene (TNT), it is frequently desirable to include a high percentage of solids such as, for example, RDX (Cyclotrimethylenetrinitramine) or HMX (Cyclotetramethylenetetranitramine). A desirable solids content may be in the range from about 70% to about 75% of the mixture or higher.
Such melt-cast loading is normally performed by heating a mixture of TNT flake and the desired solids of relatively high melting point to a temperature exceeding about 85.degree. C. and most preferably about 100.degree. C. at which temperatures the TNT is liquefied, stirring the mixture to maintain the solids in suspension and then pouring the resulting mixture, usually employing a funnel or other aid, into a mold, such as shaped charge casing.
At high solids content above, for example, 70%, the mixture has a viscosity high enough to interfere with pouring and, in addition, tends to entrap air during pouring to produce resulting cavitation and discourages the settling of solid particles toward the shaped charge liner as may be desirable in some circumstances. The presence of porosity in the solidified cast charge leads to weaknesses in the charge which may permit unintentional initiation of the explosive by impact or by adiabatic compression upon firing of the charge from a weapon.
One method which has been employed to improve pourability is to dilute the mixture with sufficient TNT to reduce the solids content to 60%. This lowers the viscosity and the air entrapment during pouring and permits more of the solid particles, and particularly the coarse component of the solid particles, to settle toward the bottom of the mold which may be arranged to be the region where highest solids content is desired. Vibration may be employed with a prolonged heating period of the poured but not solidified explosive to encourage settling of solids. This method has permitted the achievement of a solids content as high as 85% at the bottom of the charge. However, this method requires a large riser in which the solids content is predominantly finer particles with a much lower proportion of solids than is desired in the main part of the charge. This riser represents wasted material.
A further method to increase the solids content includes pressing of a fine screen into the molten mixture thus forcing solid particles ahead of the screen while allowing the liquid TNT to rise through the screen. This method has also achieved a solid content of over 85% at the base of the charge. This method requires a significant time to accomplish and thus presents a production problem for quantity production of conditions. Furthermore, the shape or other configuration of the charge may militate against use of this approach.